Kinases, phosphorylases, and phosphatases are important classes of enzymes that catalyze reactions involving phosphate groups. These enzymes have appeared in many MCAT passages.

Kinases catalyze the transfer of a phosphoryl group from ATP to an acceptor. For example, in the first reaction of glycolysis, hexokinase catalyzes the transformation of glucose to glucose 6-phosphate (an interesting example of metal ion coordination to facilitate reactivity occurs with Mg2+ (or Mn2+) in kinase shielding the negative charges of ATP readying the phosphate groups for nucleophilic approach).

Phosphorylases carry out cleavage similar to hydrolysis but employ orthophosphate instead of water, as in glycogen breakdown.

Phosphatases hydrolyze phosphoryl groups. Reversible phosphorylation, such as in glycogen metabolism, plays a central roll in regulation, with phosphatases often acting to reverse the effects of kinases.